U.S. patent number 5,472,344 [Application Number 08/190,101] was granted by the patent office on 1995-12-05 for expansion screw for tooth adjustment.
This patent grant is currently assigned to Dentaurum J.P. Winkelstroeter KG. Invention is credited to Friedrich Binder, Horst Kalytta, Manfred Rapp, Friedrich-Wilhelm Rohlcke, Berthold Walter.
United States Patent |
5,472,344 |
Binder , et al. |
December 5, 1995 |
Expansion screw for tooth adjustment
Abstract
Expansion screw for tooth adjustment having two expansion screw
body members each embeddable in a plastic palate plate, these body
members being provided with retention grooves for anchoring in the
plastic of these palate plates, also having a threaded spindle and
two guide pins, wherein the threaded spindle has spindle sections
with opposite threads on either side of a central section, these
spindle sections engaging in corresponding threaded bores of the
expansion screw body members, and wherein the latter have guide
openings for the passage of the guide pins extending parallel to
the threaded spindle. In order to reduce the size of the two
expansion screw body members, the latter are of a hat-shaped design
in the side view and provided at their central regions with
retention grooves and, in addition, at their facing inner end faces
with recesses for accommodating the central section of the threaded
spindle, these recesses being designed such that these end faces
can abut on one another when the threaded spindle is turned and
that in this state of the expansion screw the central section of
the threaded spindle provided with a tool attachment point is
accessible from the outside.
Inventors: |
Binder; Friedrich (Kieselbronn,
DE), Kalytta; Horst (Pforzheim, DE), Rapp;
Manfred (Pforzheim, DE), Rohlcke;
Friedrich-Wilhelm (Kampfelbach-Bilfingen, DE),
Walter; Berthold (Remchingen-Singen, DE) |
Assignee: |
Dentaurum J.P. Winkelstroeter
KG (Ispringen, DE)
|
Family
ID: |
6437701 |
Appl.
No.: |
08/190,101 |
Filed: |
February 2, 1994 |
PCT
Filed: |
July 27, 1992 |
PCT No.: |
PCT/EP92/01698 |
371
Date: |
February 02, 1994 |
102(e)
Date: |
February 02, 1994 |
PCT
Pub. No.: |
WO93/02629 |
PCT
Pub. Date: |
February 18, 1993 |
Foreign Application Priority Data
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|
|
|
|
Aug 3, 1991 [DE] |
|
|
41 25 853.3 |
|
Current U.S.
Class: |
433/7 |
Current CPC
Class: |
A61C
7/10 (20130101) |
Current International
Class: |
A61C
7/10 (20060101); A61C 7/00 (20060101); A61C
007/00 () |
Field of
Search: |
;433/6,7 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0304756 |
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Aug 1988 |
|
EP |
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824832 |
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Jul 1949 |
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DE |
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1932323 |
|
Jun 1965 |
|
DE |
|
2712696 |
|
Sep 1978 |
|
DE |
|
2722611 |
|
Nov 1978 |
|
DE |
|
526301 |
|
Sep 1972 |
|
CH |
|
641139 |
|
Aug 1950 |
|
GB |
|
718385 |
|
Nov 1954 |
|
GB |
|
Primary Examiner: Lucchesi; Nicholas D.
Attorney, Agent or Firm: Leydig, Voit & Mayer, Ltd.
Claims
We claim:
1. An expansion screw for tooth adjustment having two expansion
screw body members each embeddable in a plastic palate plate, the
body members being provided with retention means for anchoring in
the plastic of said palate plate, also having a threaded spindle
and at least one guide pin, wherein the threaded spindle has
spindle sections with opposite threads on either side of a central
section provided with a point of attachment for a tool for turning
the threaded spindle, the spindle sections engaging in channels
provided with corresponding internal threads in the expansion screw
body members for altering the distance of the two expansion screw
body members from one another, and wherein the expansion screw body
members have guide openings for the passage of said at least one
guide pin extending parallel to the threaded spindle, each
expansion screw body member being stepped at an outer end face
remote from an outer end face of the other body member such that a
first region of said expansion screw body member accommodating one
of the channels protrudes in the longitudinal direction of the
threaded spindle beyond a second region of said expansion screw
body member accommodating the guide opening for said at least one
guide pin wherein the retention means are arranged at the first
regions of the two expansion screw body members, and the channels
are designed at facing inner end faces of the two expansion screw
body members to accommodate the central section of the threaded
spindle whereby in a non-expanded initial state of the expansion
screw said inner end faces are adapted to abut at least almost
against one another, and wherein the expansion screw body members
have at least one recess through which, in the initial state of the
expansion screw, the tool attachment point of the threaded spindle
is accessible from the outside of the expansion screw.
2. The expansion screw as defined in claim 1, wherein during the
initial state of the expansion screw the inner end faces of the
expansion screw body members abut at least almost on one another in
the region of the guide openings.
3. The expansion screw as defined in claim 1, wherein the channel
of at least one of the expansion screw body members has adjacent
its inner end face a recess enlarged in relation to its internal
thread for accommodating the central section of the threaded
spindle.
4. The expansion screw as defined in claim 3, wherein the channels
of the two expansion screw body members each comprise an enlarged
recess for respectively accommodating half the central section of
the threaded spindle.
5. The expansion screw as defined in claim 1, wherein the second
region of each of said body members has a wall thickness measured
in the longitudinal direction of the spindle and wherein the first
region of each of said body members protrudes beyond the second
region by at least said wall thickness.
6. The expansion screw as defined in claim 1, wherein two guide
pins arranged on either side of the threaded spindle are provided
and each expansion screw body member has an approximately
hat-shaped cross section along the plane defined by the
longitudinal central axes of the threaded spindle and at least one
of the guide pins.
7. The expansion screw as defined in claim 1, wherein said at least
one guide pin is designed as a cylindrical body, having two ends
deviating in shape from that of the cylindrical body to form stops
interacting with the outer end faces of the expansion screw body
members.
8. The expansion screw as defined in claim 1, wherein in said
initial state of the expansion screw, an interstice is provided
between said inner end faces of the body members, said expansion
screw further comprising an expansion screw holder enclosing at
least partially the expansion screw body members drawn together,
said holder lying completely outside the interstice between the
expansion screw body members.
9. The expansion screw as defined in claim 8, wherein the expansion
screw holder covers the tool attachment point of the threaded
spindle.
10. The expansion screw as defined in claim 8 wherein the expansion
screw holder covers the interstice between the expansion screen
body members.
11. The expansion screw as defined in claim 8 wherein the expansion
screen holder covers the interstice between the expansion screen
body members at least in the initial state of the expansion
screw.
12. The expansion screw as defined in claim 1, wherein the two
expansion screw body members are of substantially identical outer
shape.
13. The expansion screw as defined in claim 1, wherein at least one
retention means comprises an annular groove provided at the
circumference of the first region of each expansion screw body
member.
14. The expansion screw as defined in claim 1, wherein the threaded
spindle and said at least one guide pin are of equal length.
15. The expansion screw as defined in claim 1, wherein the threaded
spindle is longer than said at least one guide pin.
16. The expansion screw as defined in claim 1, wherein said guide
openings define guide faces for said at least one guide pin and
said guide faces end at guide opening neighboring regions of said
inner end faces, said regions adapted to abut one another in the
initial state of the expansion screw.
17. The expansion screw as defined in claim 1, further comprising a
spindle head formed by said central section of the threaded
spindle, the thickness of said spindle head measured in the
longitudinal direction of the threaded spindle being at least equal
to the sum of the thicknesses of the second regions of the two
expansion screw body members adjacent one another.
Description
FIELD OF THE INVENTION
The invention relates to an expansion screw for tooth adjustment
having two expansion screw body members each embeddable in a
plastic palate plate, these body members being provided with
retention means for anchoring in the plastic of these palate
plates, also having a threaded spindle and at least one guide pin,
wherein the threaded spindle has spindle sections with opposite
threads on either side of a central section provided with a point
of attachment for a tool for turning the threaded spindle, these
spindle sections engaging in channels provided with corresponding
internal threads in the expansion screw body members for altering
the distance of the two expansion screw body members from one
another, and wherein the expansion screw body members have guide
openings for the passage of the guide pin extending parallel to the
threaded spindle.
BACKGROUND OF THE INVENTION
There are two current types of expansion screws with which the
forces exerted by the expansion screw are to be transferred in
various ways onto the tooth or teeth, the position of which is
intended to be corrected: In expansion screws of a first type, the
relevant expansion screw is embedded in a palate plate cast from
casting resin and divides the palate plate into two parts such that
one of the two expansion screw body members of the expansion screw
is located in each palate plate part and so the distance of the two
palate plate parts from one another can be altered by turning the
threaded spindle of the expansion screw. During the casting of the
palate plate, for example, clasp-like anchoring elements are
secured therein and these elements engage on teeth so that the
forces of the expansion screw are transferred to the relevant teeth
via the palate plate parts. Such an expansion screw of this type
is, for example, illustrated in FIG. 3 of DE-PS 33 01 753. With the
second type of expansion screw, two rods or stiff wires are
secured, in particular welded, to each of the two expansion screw
body members and the relevant expansion screw body member can be
anchored by these rods or wires directly onto metal bands secured
to the teeth. An expansion screw of this type is illustrated, for
example, in FIG. 2 of U.S. Pat. No. 4,917,601.
When in the above or in the following mention is made of a tooth
adjustment or of the correction of the position of a tooth or
several teeth, this is to be understood as also including, for
example, the separation of the mid-palatal suture since a
mid-palatal suture separation also results, of course, in an
alteration of the tooth position.
SUMMARY OF THE INVENTION
As expressed at the outset, the present invention deals with
expansion screws of the first type, i.e. with expansion screws
which are used in conjunction with a plastic palate plate, during
the production of which the two expansion screw body members are
embedded in the casting resin of the palate plate.
An expansion screw of the type specified at the outset is known;
this known expansion screw corresponds to that according to DE-PS
33 01 753 but is provided with retention means in the form of
short, straight grooves which--in the side view of the expansion
screw--are arranged in front of and behind the threaded spindle as
well as at the outer narrow sides of the two expansion screw body
members.
This known expansion screw has two guide pins arranged on either
side of the threaded spindle and these pins are guided for
displacement in guide openings of both expansion screw body
members. The latter have a rectangular cross section along the
plane defined by the longitudinal central axes of the threaded
spindle and guide pins, and the central section of the threaded
spindle has the shape of a thickened, circular-cylindrical collar
(spindle head) with a transverse bore for the insertion of a pivot
pin, with which the threaded spindle can be turned. The guide
openings of the two expansion screw body members each have the
shape of a recessed bore, the first section of which facing the
spindle head has a diameter corresponding to the diameter of the
guide pins and is followed by a bore section of larger diameter,
into which head-shaped, thickened ends of the guide pins, which act
as stops, can be inserted when the expansion screw body members are
moved apart due to turning of the threaded spindle until these
stops abut on the shoulders which form the second bore sections at
the transition to the first bore sections. In the case of this
known expansion screw, the maximum path of an expansion screw body
member is equal to half the length of a guide pin (calculated
without its thickened end) less the length of the first bore
section of smaller diameter and less half the width of the spindle
head (measured in the longitudinal direction of the threaded
spindle), provided that both guide pins are of equal length and at
the most as long as the threaded spindle.
Since expansion screws of this type are worn in the mouth where
every millimeter is of importance in view of the cramped spatial
conditions, depending on the position of the tooth or teeth which
is or are to be corrected, the object underlying the invention was
to provide an expansion screw of the type mentioned at the outset
which is smaller than the known expansion screw described above, at
a predetermined maximum path of expansion, without the smaller size
impairing the function of the expansion screw (in this respect, the
maximum path of expansion is to be understood as the maximum
possible alteration in the distance between the facing inner end
faces of the expansion screw body members).
This object may be accomplished in accordance with the invention in
that the expansion screw body members are stepped at their outer
end faces remote from one another such that a first region of each
expansion screw body member accommodating the channel protrudes in
the longitudinal direction of the threaded spindle beyond a second
region of the relevant expansion screw body member accommodating
the guide opening for the guide pin, that the retention means are
provided at the first regions of the two expansion screw body
members, that the channels are designed at the facing inner end
faces of the two expansion screw body members to accommodate the
central section of the threaded spindle and so in an initial state
of the expansion screw these inner end faces are adapted to abut at
least almost against one another, and that the expansion screw body
members have at least one recess, the tool attachment point of the
threaded spindle being accessible from the outside through this
recess in the initial state of the expansion screw.
While the expansion screw body members of both the expansion screw
according to DE-PS 33 01 753 discussed above and the expansion
screw according to U.S. Pat. No. 4,917,601 are block-shaped in
design, i.e. rectangular in the side view, the inventive expansion
screw is much more delicate due to its stepped expansion screw body
members. In addition, a relatively large gap is avoided between the
expansion screw body members due to the inventive design of the
expansion screw--if special measures are not taken, the casting
resin flows into this gap in the known expansion screws during
production of the palate plate and this can have a disadvantageous
effect on the actuation of the threaded spindle. Finally, it is
also possible to save on material for the expansion screw body
members during the production of the inventive expansion screw and
this is of importance, in particular, when the body members are
produced from an expensive material. Any saving on material also
results, of course, in a reduction in the weight of the expansion
screw. On the other hand, the reduction in size of the expansion
screw body does not have any disadvantageous effects on the quality
of the sliding guidance of the guide pin in the guide openings of
the expansion screw body members owing to the inventive arrangement
of the retention means at the first regions of the two expansion
screw body members comprising the threaded spindle. Considerable
forces are to be transferred from the expansion screw body members
to the parts of the palate plate. If retention means were provided
at the relatively thin second regions of the expansion screw body
members, in particular at the outer narrow sides of these second
regions of the expansion screw body members, there would be the
risk, due to the forces to be transferred, of the narrow second
regions of the expansion screw body members being deflected or even
bent in relation to the first regions comprising the threaded
spindle and, therefore, the guide openings being canted on the
guide pin as a result of these forces.
Certain features of the inventive solution are, indeed, known from
the state of the art but the known expansion screws could still not
anticipate the inventive combination because none of the known
expansion screws teaches how an expansion screw which is to be
embedded in a palate plate is to be designed in order for it to be
of as delicate a construction as possible, on the one hand, but, on
the other hand, to ensure a good sliding guidance for the guide pin
despite the considerable forces to be transferred from the
expansion screw to the palate plate parts. With respect to the
state of the art, reference is also made in detail to the following
known expansion screws:
The expansion screw according to U.S. Pat. No. 4,917,601 is, as
already mentioned, an expansion screw having rods welded to its
expansion screw body members, with which the expansion screw is
intended to be anchored directly to metal bands attached to the
teeth. The two expansion screw body members of this known expansion
screw have at their facing ends recesses for accommodating the
spindle head of the threaded spindle so that in the initial state
of the expansion screw the inner end faces of the two expansion
screw body members abut on one another and the recesses form a
window, through which, in the initial state of the expansion screw,
the tool attachment point of the spindle head is accessible from
the outside. As already mentioned, the two expansion screw body
members of this known expansion screw are, however, of a block-type
design, i.e. approximately rectangular in the side view, and
retention means are not provided on the expansion screw body
members because the latter are anchored by the specified rods
directly on teeth.
The same is true of another known expansion screw, which results
from DE-PS 27 12 696 and essentially differs from the expansion
screw according to U.S. Pat. No. 4,917,601 only in that two of the
four rods serving to directly anchor the expansion screw to teeth
form guide pins at the same time.
DE-GM 1 932 323 discloses an expansion screw provided for embedding
in a plastic palate plate, the expansion screw body members of
which accommodate a small plate-like expansion screw holder between
them when the expansion screw is embedded in a palate plate. This
holder encloses the spindle head of the threaded spindle such that
the expansion screw body members can be brought closer to one
another only to such an extent that the distance between them is
equal to the thickness of the expansion screw holder or equal to
the axial length of the spindle head. The two expansion screw body
members of this known expansion screw are of an approximately
"hat-shaped" design in the side view and each have a central first
region which comprises the threaded spindle as well as two flat
second regions which extend away from this central region towards
the side and have guide openings for guide pins. Retention means
are not provided at all in this known expansion screw.
Finally, DE-PS 824 832 discloses an expansion screw of a completely
different type having two expansion screw body members which are
block-shaped in design, i.e. approximately rectangular in the side
view, and which each have at their facing inner ends a recess for
accommodating the spindle head of the threaded spindle. These
recesses are each followed by a stepped bore, the inner part of
which, which is smaller in diameter, is penetrated by the threaded
spindle and the outer part of which, which is larger in diameter,
bears a nut for the threaded spindle which is pressed by a
compression spring against the shoulder formed by the bore. In
order to hold the two pressure springs in the expansion screw body
members, a cover is placed on each of their outer end faces which
face away from one another. One of these covers is penetrated by
two guide pins which are secured in position in the expansion screw
body member belonging to the other cover. Annular grooves extend
around the two block-shaped expansion screw body members and these
grooves form retention means for anchoring the expansion screw body
members in the parts of a palate plate. An expansion screw holder
is not provided in this known expansion screw.
The inventive solution also allows the maximum path of expansion of
the inventive expansion screw to be increased, by corresponding
dimensioning of the thickness (measured in the longitudinal
direction of the threaded spindle) of the second regions of the
expansion screw body members accommodating the guide openings for
the guide pin or the guide pins, such that it exceeds that of the
known expansion screw according to DE-PS 33 01 753 (when the length
of threaded spindle and guide pin or guide pins is the same),
namely by the width of the central section of the threaded spindle
(of the spindle head of the known expansion screw) measured in the
longitudinal direction of the threaded spindle, because in the
initial state of the inventive expansion screw its expansion screw
body members can completely accommodate the central section of the
threaded spindle--it is then only necessary to design the expansion
screw body members such that the tool attachment point of the
threaded spindle is still adequately accessible for a corresponding
tool when the two expansion screw body members have been brought so
close to one another that they abut on one another.
When it has been stated in the above that the facing inner end
faces of the two expansion screw body members are intended to be
able to abut on one another, this certainly does not mean that
these inner end faces each form a plane or even a plane extending
at right angles to the spindle axis, and in this respect reference
can be made to the embodiments of the inventive expansion screw
which will be described at a later stage.
In the case of the inventive expansion screw, the guide pin is or
the guide pins are intended to be freely displaceable in both
expansion screw body members, when any end stops which may be
provided are left out of account.
The invention does not presuppose that the central section of the
threaded spindle which is provided with the tool attachment point
is designed as a thickened spindle head; this central section of
the threaded spindle could have the same or even a slightly smaller
outer diameter than the threaded sections provided with threads
since it is only important that the recess in at least one of the
two expansion screw body members forms a type of window, through
which a tool can be applied to the threaded spindle for turning
this spindle, on at least one side, preferably on both sides of the
expansion screw body members which have been brought together.
A minimum length of the guide pin or the guide pins (at a
predetermined maximum path of expansion of the expansion screw)
results when in the initial state of the expansion screw the inner
end faces of the expansion screw body members abut on one another
in the region of their guide openings.
The sections of the threaded spindle provided with opposite threads
could be immediately adjacent one another without a thread-free
region of the threaded spindle when a transverse bore is selected
as tool attachment point. In this case, the internal threads of the
expansion screw body members could extend as far as their facing,
inner end faces. In inventive expansion screws, in which the
central section of the threaded spindle is designed as a thickened
spindle head, the channel of at least one of the expansion screw
body members has, however, adjacent its inner end face a recess for
accommodating the central section of the threaded spindle which is
enlarged in relation to its internal thread. In this connection,
reference is made to the following: In principle, the only
important feature for the functioning of an expansion screw is the
change in the distance of the two expansion screw body members from
one another; for this reason, it would, for example, also be
possible, in the initial state of an expansion screw, to
accommodate the spindle head of its threaded spindle completely in
one of the two expansion screw body members, as is shown, for
example, in DE-PS 27 12 696. It is then sufficient to provide only
one of the two expansion screw body members with a recess for
accommodating the central section of the threaded spindle which is
enlarged in relation to its internal thread and also to provide a
recess, through which the tool attachment point of the threaded
spindle is accessible from the outside in the initial state of the
expansion screw, only in this expansion screw body member. For the
reasons explained above, the two opposite threads of the threaded
spindle need not have the same thread pitch (the same applies to
the internal threads of the expansion screw body members). This
shows that the central section of the threaded spindle need not be
located exactly in the center of the threaded spindle and in the
initial state of the expansion screw can be inserted into only one
of the two expansion screw body members. In a preferred embodiment
of the inventive expansion screw, the channels of both expansion
screw body members do, however, have an enlarged recess for
respectively accommodating half the central section of the threaded
spindle designed as a spindle head.
The above explanations show that an essential constructional
feature of the inventive expansion screw can also be defined such
that the channels for the threaded spindle, which are provided in
the expansion screw body members, are designed such that in the
initial state of the expansion screw they accommodate the central
section of the threaded spindle except for a window, through which
the tool attachment point of the threaded spindle is accessible
from the outside, and that the guide surfaces of the guide openings
for the guide pin or the guide pins extend as far as those regions
of the inner end faces of the expansion screw body members which
abut at least almost against one another in the initial state of
the expansion screw.
With the inventive expansion screw embodiments are also preferred,
in which two guide pins arranged on either side of the threaded
spindle are provided; in this case, it is recommended that the
expansion screw be designed such that each expansion screw body
member has an approximately hat-shaped cross section along the
plane defined by the longitudinal central axes of threaded spindle
and at least one of the guide pins. The second regions of the
respective expansion screw body member accommodating the guide
openings then form, so-to-speak, the brim of the hat.
It is particularly advantageous for the expansion screw to be
designed to be symmetrical to a longitudinal central plane which
extends through the longitudinal central axis of the threaded
spindle and at right angles to that plane which is defined by the
longitudinal central axes of threaded spindle and guide pins.
According to a further feature of the invention, the expansion
screw is designed to be symmetrical to the plane last
mentioned.
To prevent the guide pins from falling out of the expansion screw
body members, an embodiment is recommended, in which the guide pin
is designed as a cylindrical body, the two ends of which deviate in
design from the cylindrical shape to form stops interacting with
the outer end faces of the expansion screw body members. In this
respect, it is recommended that these stops be formed by cutting
notches into the end faces of the guide pins.
In order to hold an expansion screw in the correct position during
the casting of the palate plate it is customary for the expansion
screw to be provided with a so-called expansion screw holder which
is a small plastic plate which has openings for the passage of the
threaded spindle and the guide pins and comprises the spindle head
in the known expansion screws and is arranged between the expansion
screw body members brought together to the smallest possible
distance between them. In this connection, reference is, however,
made to the fact that an expansion screw holder is not absolutely
necessary because the expansion screw could also be fixed with
adhesive wax to the mold for the casting of the palate plate and
the spindle head could be covered with wax to prevent its tool
attachment point being covered over by the casting resin.
The invention now suggests a completely different course to follow
if an inventive expansion screw is intended to be provided with an
expansion screw holder: An expansion screw holder is suggested
which encloses the expansion screw body members drawn together and
which lies completely outside the interface or interstice between
the expansion screw body members and preferably covers the tool
attachment point of the threaded spindle. This means that the
expansion screw holder does not obstruct any complete drawing
together of the two expansion screw body members. For particularly
advantageous embodiments, it is suggested that the expansion screw
holder be designed such that it completely encloses the two
expansion screw body members, which are drawn together, in the
region of the interstice located between them and thereby covers
the window or windows which is or are formed by the recesses
provided on the inner end faces of the expansion screw body
members. The expansion screw holder then prevents the casting resin
from penetrating the interstice between the two expansion screw
body members as well as any covering over of the tool attachment
point of the threaded spindle by the casting resin.
If, in the case of an expansion screw having such an expansion
screw holder, retention means were to be provided on the outer
narrow sides of the relatively thin, second regions of the
expansion screw body members, these retention means would be
covered by the expansion screw holder at least to a large extent
which would preclude a good anchoring of the expansion screw body
members in the palate plate parts. Owing to the inventive
arrangement of the retention means at the first regions of the
expansion screw body members enclosing the threaded spindle, the
expansion screw body members may be well anchored in a palate plate
even though the expansion screw holder encloses the expansion screw
body members drawn together and is not, as is the case in the known
expansion screws, located between the expansion screw body
members.
In order to simplify the assembly of the expansion screw together
with the expansion screw holder and to ensure that the expansion
screw holder reliably covers the tool attachment point of the
threaded spindle, it is, finally, recommended that at least one of
the two expansion screw body members be provided with a stop for
the expansion screw holder which acts in the direction of the
threaded spindle axis.
A particularly efficient production of the inventive expansion
screw is made possible by an embodiment, in which the two expansion
screw body members are of identical design, apart from their
internal threads and a stop possibly provided for the expansion
screw holder.
The retention means could have the shape of knurled zones or, for
example, etched, rough surface regions. With a view to a
particularly good anchoring of the expansion screw body members in
the palate plate parts, groove-like retention means are, however,
preferred. In this respect, it has proven to be particularly
advantageous and effective for the retention grooves to be designed
as annular grooves which extend around the first regions of the two
expansion screw body members which comprise the threaded
spindle.
Additional advantages, features and details of the invention result
from the following description as well as the attached drawings of
three particularly preferred embodiments of the inventive expansion
screw; in the drawings:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a longitudinal section through the first expansion
screw with attached expansion screw holder, namely a section along
line 1--1 in FIG. 2;
FIG. 2 shows a section through this expansion screw with expansion
screw holder along line 2--2 in FIG. 1;
FIG. 3 shows the expansion screw body member illustrated at the top
of FIG. 1 in the same section as in FIG. 1;
FIG. 4 shows this expansion screw body member seen in
the direction of arrow "A" in FIG. 3;
FIG. 5 is a plan view onto this expansion screw;
FIG. 6 is an illustration of the second embodiment of the inventive
expansion screw corresponding to FIG. 1, and
FIG. 7 is an illustration of the third embodiment corresponding to
FIG. 1.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
The expansion screw according to FIGS. 1 to 5 consists of a first
and a second expansion screw body member 10 and 12, respectively, a
threaded spindle 14, two guide pins 16 and an expansion screw
holder 18.
The threaded spindle 14 has a thickened spindle head 14a which is
centrally arranged according to the invention and has two centrally
arranged transverse bores 14b extending at right angles to one
another as well as two threaded sections 14c and 14d arranged on
either side of the spindle head and having opposite threads 14e and
14f of the same pitch. The latter end at transition regions 14g
which are designed to be circular-cylindrical and border on the
spindle head 14a, which is designed to be rotationally symmetrical
to the spindle axis 14h, and preferably have the same external
diameter as the threaded sections 14c and 14d. Instead of the
illustrated transition region 14g, a groove (not shown) could also
be used in which the adjacent thread 14e or 14f ends.
In the illustrated, preferred embodiment, the guide pins 16 are
circular-cylindrical in design--apart from their end
regions--although they could also have a different cross section,
i.e. they could, for example, be designed in the shape of a prism.
Following the assembly of the expansion screw, notches 16a are cut
into the end faces of the guide pins 16 and these result in a
slight increase in the circumferential dimensions of the ends of
the guide pins so that these ends form stops which have been
designated 16b in FIG. 1--the deviations in the outer contour of
these stops in comparison with the outer contour of the actual
guide pins 16 are so slight that they are not apparent in FIG.
1.
The first expansion screw body member 10, illustrated at the top in
FIG. 1, will now be explained in greater detail on the basis of
FIGS. 3-5.
This expansion screw body member has on each side of a first region
20, which is of a neck-shaped design in accordance with the
invention and in which a channel 21 provided with an internal
thread 22 is located, a second region 24 having a guide opening 26
for one of the guide pins 16. A recess 30 extends into the
expansion screw body member from an inner end face 28 of the
expansion screw body member located in the interior of the
expansion screw. The shape of this recess is, in accordance with
the invention, adapted to that of the spindle head 14a such that
the recess 30 can accommodate approximately half the spindle head
14a and the latter can turn in this recess. A recess 32 is provided
between the internal thread 22 and the recess 30 and this is
adapted to the dimensions of the transition region 14g of the
threaded spindle 14 so that this transition region can turn in the
recess 32. At the outer end face of the expansion screw body member
10 lying opposite the inner end face 28 the guide openings 26 are
provided with countersinks 34 into which the stops 16b of the guide
pins 16 can enter. Finally, a circular ring-shaped retention groove
36 is provided in the outer circumference of the neck-shaped first
region 20.
In accordance with the invention, the expansion screw body member
10 is provided on each of its two broad sides (upper and lower
sides according to FIG. 4) with a recess 38 which has been
produced, in particular, as a recess manufactured with a radius R.
When the expansion screw body members 10 and 12 are drawn together,
i.e. abut on one another (as illustrated in FIG. 1), these recesses
38 of the two expansion screw body members form on each expansion
screw side a type of window, through which the spindle head 14a is
exposed, so that a pin or another suitable tool can be inserted
through this window into one of the transverse bores 14b and, with
the aid of this pin, the threaded spindle 14 can be turned through
an angle of rotation of, for example, 90.degree..
The recesses 38 can extend into the expansion screw body member 10
in the direction of the spindle axis 14h, proceeding from the inner
end face 28, to such an extent that the spindle head 14a is exposed
in its entire width (measured in the direction of the spindle axis)
through the windows formed by the recesses 38. However, embodiments
are preferred, in which the recesses 38 extend into the expansion
screw body member 10 in axial direction only to such an extent that
the windows formed by these recesses 38 only expose that region of
the spindle head 14a in which the transverse bores 14b are located,
i.e. the axial extension of these windows is equal to the diameter
of the transverse bores 14b or only slightly greater.
The second expansion screw body member 12 is identical to the first
expansion screw body member 10 as so far described in the above,
except for opposite internal threads 22. The difference between the
two expansion screw body members 10 and 12 consists only in at
least one stop or preferably two stops 40 formed on the first
expansion screw body member 10 for the expansion screw holder 18 in
order to ensure that the latter covers the interstice 42 between
the two expansion screw body members 10 and 12 as well as the two
windows formed by the recesses 38. When the expansion screw is
embedded in a palate plate produced from a casting resin, the
expansion screw is in the state shown in FIG. 1, i.e. the two
expansion screw body members 10 and 12 are drawn together and abut
on one another and so it can be ensured due to the covering formed
by the expansion screw holder 18 that no casting resin can flow
into the interstice 42 and into the transverse bores 14b.
The expansion screw holder 18 shown in FIGS. 1 and 2 has, as
already mentioned, the shape of a small plastic plate with an
opening 50, the shape of which corresponds to the outer contour of
the expansion screw body formed by the two expansion screw body
members 10 and 12, namely the outer contour when viewing the
expansion screw body in the direction of the spindle axis 14h.
The expansion screw holder 18 is, of course, removed before the
expansion screw is actuated. By turning the threaded spindle 14 the
two expansion screw body members 10 and 12 can then be moved apart
to such an extent until the stops 16b of the guide pins 16 enter
the countersinks 34 of the two expansion screw body members 10, 12
and come to rest on these expansion screw body members. For this
purpose, the threaded spindle 14 must, of course, be of such a
length that its threaded sections 14c and 14d still engage in the
internal threads 22 of the two expansion screw body members 10,
12.
FIG. 6 shows the second embodiment in a section corresponding to
FIG. 1, and the various parts of this expansion screw have been
designated with the same reference numerals as in FIG. 1 but with
the addition of a prime. Whereas, however, the threaded spindle 14
and the guide pins 16 in the embodiment according to FIG. 1 are of
the same length because, in accordance with the invention, the
guide length "x" of the guide openings 26 corresponds in this
embodiment to half the overall length of the spindle head 14a and
the two transition regions 14g (measured in the direction of the
spindle axis 14h), i.e. in other words the length of that part of
the corresponding expansion screw body member which is not provided
with the internal thread 22, the threaded spindle 14' of the
embodiment according to FIG. 6 is, according to the invention,
longer than the guide pins 16', namely for the following reason: In
the embodiment according to FIG. 6, the guide length "x'" of the
guide openings 26' of the expansion screw body members 10', 12' is,
according to the invention, smaller than the measurement "y'",
namely by the measurement "z'", and the thread 14e' or 14f',
respectively, of the threaded spindle 14' is longer than the
corresponding thread of the threaded spindle 14 by this measurement
"z'". This means that the threaded spindle 14' is longer than the
guide pins 16' by the double amount of this measurement "z'".
When mention is made in the above of the length of the threaded
spindle and the length of the guide pins, the lengths of the stops
16a and 16a', respectively, of the guide pins and the lengths of
the thread-less end regions 14i and 14i', respectively, of the
threaded spindle have been left out of consideration just as much
as any narrow gap which may be present between the two expansion
screw body members instead of the interstice 42 or 42' and which
can result, in unfavourable cases, due to angular offset
displacements of the threads 14e, 14f or 14e', 14f'and/or of the
internal threads 22 or 22'.
Under this precondition, a comparison of the two embodiments
according to FIGS. 1 and 6 results in the fact that, according to
the invention, the length L of the threaded spindle is
wherein 1 is the length of the guide pins, x the guide length of a
guide opening 26 (disregarding the depth of a countersink 34a at
the inner end face 28) and y half the overall length of the
thread-less central section of the threaded spindle, whereby in the
embodiments illustrated this thread-less central section is
composed of the spindle head 14a or 14a' and the thread-less
transition regions 14g or 14g'.
Whereas the embodiments according to FIGS. 1 to 6 result in
particularly large paths of expansion (at predetermined lengths of
threaded spindles and guide pins), the expansion screw body members
of the embodiment according to FIG. 7 have an increased stability.
In FIG. 7, all the parts have been given the same reference
numerals as in FIGS. 1 to 5 but with the addition of a double prime
so that, in the following, only the differences between the
embodiment according to FIG. 7 and the embodiment according to
FIGS. 1 to 5 will be explained.
In the embodiment according to FIG. 7, namely, half the axial
length of the spindle head 14a" plus the axial length of a
thread-less transition region 14g", i.e. the length y", is smaller
than the guide length x" (also when taking a countersink 34" into
consideration) in order to increase the rigidity at the transition
from the second regions 24" to the first region 20" of the
expansion screw body members. Moreover, an increase in the
thickness of the second regions of the expansion screw body members
results in the advantage that the latter can be reliably gripped at
their side edges by automatic gripping means during automatic
assembly of the expansion screw.
In this embodiment, the axial length of the thread-less central
section of the threaded spindle is, therefore, somewhat larger than
the sum of the thicknesses of the second regions 24" of the two
expansion screw body members.
* * * * *